Method for reducing nitroarylarsonic acids



Patented Mar. 24, 1931 UNITED STATES PATENT oFFicE CARL OECHSLIN, OF ABLON, FRANCE, ASSIGNOR TO LES ETABLISSEMENTS POULENG FRERES, A CORPORATION OF FRANCE METHOD FOR REDUCING NITROAEYLARSONIC ACIDS No Drawing. Application filed November 2, 1927, Serial No. 230,692, and in France November 2, 1926.

A certain number of methods for reducing nitroarylarsonic acid to the corresponding amines are already known. Certain of these methods effect the reduction without acting on the arsonic acid group, while others simultaneously reduce both the nitro group and the arsonic acid. Among the former of these two methods, there is the one described by Benda, Berichte, vol. 44, p. 3302, 1911, making use of ferrous salts, another employing so dium hydrosulphite or sodium amalgam (D. R. P. 224,953), still another utilizing electrolysis (D. P. Anm. K. 51.745 class 12g) others still using, carbohydrates and an al- 15 kali (D. P. AIIHLE. 28.313, class 12g), palladium and hydrogen and sulphides followed by desulphurization. Among the methods effecting a double reduction may be mentioned those employing hydrosulphite and those involving the use of zinc. The latter of these two has been generally considered to be particularly effective in simultaneous reductions ofthe nitro and arsonic acid groups to the corresponding aminoarylarsines (D. R. P. 251,571). The reaction has been carried out in acid solution since it is known that the arsonic acid groups is less resistant in an acid medium (sulphurous acid, for example) than in an alkaline or neutral medium of the type furnished by sodium sulphite.

It seemed, therefore, that a similar difl'erence would he found in the action of metallic reducing agents. With this idea in mind, the action of zinc in alkaline solution was tried on various nitroarylarsonic acid and it was 7 found that the reduction of the nitro group was practically theoretical, and that the aminoarylarsonic acid resulting from the reaction could be easily isolated, the zinc being recovered in the form of some zinc salt.

The method may, by wayof illustration, be carried out as follows: 315 gms. of p-hydroxym-nitrophenylarsonic acid contained in 500 0.0. of water are treated with 1,145 0.0. of

45 36 Beaum caustic soda solution; 500 gms.

of powdered zinc are then added with constant stirring the temperature being maintained at 40 C. when the solution is decolorized, 1500 cc. of cold water are added and the excess zinc is separated from the mixture; the solution is then acidified with HCl until acid to Congo red, decolorized with charcoal and neutralized with NaI-ICO until feebly acid to Congo red. The amino-hydroxyphenylarsonic acid precipitates as a nearly white mass.

The mother liquors when rendered neutral to tournesol yield a precipitate of zinc salts of aminohydroxyphenylarsonic acid which may be dried, dissolved in HCl, decolorized and precipitated by NaHCO, in the manner described in the previous paragraph. The total yield of amino-hydroxyphenylarsonic acid is 90%.

The reaction may be formulated as follows- AS03151: ASOaH As an example of another type of procedure, 310 grams of p-amino-m-nitrophenylarsonic acid are treated with 500 c. c. of water and 1145 c. c. of 36 B. caustic soda; 500 gms. of powdered zinc are then. added with agitation, the temperature being maintained at 40 (reduction really begins at lower temperatures and may be carried out at temperatures as high as 6070), after decolorization the solution is diluted with 1000 o. c. ofwater and the solution filtered; the filtrate is acidified to slight acidity relatively to Congo red, and the precipitated diaminophenylarsonic acid recrystallized from hot water after decolorization by charcoal.

Having now particularly described and v ascertained the nature of my said invention, 90

and in what manner the same is to be performed, I declare that What I claim is The method of producing aminophenylarsonic acids which comprises the steps of reducing a nitrophenylarsonic acid compound With zinc in an aqueous solution of a caustic alkali at temperatures between 40 and 7 0 (3., removing the excess of zinc, neutralizing the solution, and separating the aminophenylarsonic acid precipitated.

In testimony whereof I aifix my signature.

7 CARL OECHSLIN. 

